PROGRESS WITH THE P.I ...
The P.I A can in fact fly supersonically for extended periodswithout using reheat. Since all power systems and essential ser-
vices are energized by both engines it has been found possible tocruise with one powerplant shut down (there are, of course, no
asymmetric problems). This may well be the procedure givingmaximum operational endurance. Should such a contingency
arise, it would also be possible to ferry the aircraft from one baseto another using only one engine throughout. For maximum
range at altitude—as distinct from endurance—the optimum flight-plan is sure to specify the use of both engines, shutting off one
powerplant at the end of the flight when the aircraft has descendedto a low altitude. This has been found to apply to the F-101.
The advantage of having two engines cannot be stressed toohighly, and it is a great comfort to a pilot when he is flying so
advanced an aeroplane. In single-engined machines of compar-able performance a dead-stick landing is invariably difficult and
dangerous, and the loss of the engine usually leads to a bale-out.
Further augmentation of thrust, particularly at high supersonicspeeds, can be provided by employment of reheat. Initially neither
of the P.I As had such augmentation, but the first machine,WG 760, was modified for elementary reheat trials late in 1955.
The original powerplants were replaced by specially developedSapphires incorporating afterburners with fixed-area propelling
nozzles set to give optimum thrust in the reheat condition.Although such an arrangement eliminates most of the mechanical
problems associated with variable-area nozzles it drastically re-duces the maximum thrust available in the non-reheat condition.
Thrust figures for the powerplants fitted to WG 760 may not bepublished, but it is a straightforward exercise to calculate what
they might be. Assuming that the basic engine has a dry thrustof 7,500 lb, reheat might bring this up to between 9,500 and
10,000 lb. Working backwards from the optimum size of propel-ling nozzle, the dry thrust with such an arrangement can scarcely
exceed 5,000 lb, and may be even less. This handicaps perform-ance and might even make reheat mandatory for take-off and for
much of the flight envelope.
544 FLIGHT, 26 April 1957
In a tight turn, WG 760 displays its new wing form.
The third P.I A airframe has been structurally evaluated at War-ton, and was finally tested to destruction. Last December WG 763
flew to Turnhouse Airport, Edinburgh, on a mission described as"in relation to the installation and testing of radar equipment by the
Ferranti company." For some time the same aircraft has also beenfitted with a trim, yet capacious, bulge on its underside (seen for
the first time in a photograph on p. 542). This may be a tank, or afairing for a rocket motor—or perhaps both. The trial installation
does not seem to impair the supersonic performance of WG 763,and the bulge was allowed for in the area-ruling.
Meanwhile, WG 760, the original reheat aircraft, is conductingflight trials with a slightly revised wing with a kinked leading edge.
This does not imply that the aircraft has suffered buffet or pitch-up problems similar to those encountered by aircraft of earlier
generations to which a superficially similar modification has beenmade. The new wing is intended to provide the optimum shape
of camber for achieving the maximum ceiling and the best rangeat subsonic or low supersonic speeds. Obviously such conditions
call for flight at rather greater angles of attack than the originalsupersonic design-case, and consequently require not only a fair
leading-edge radius towards the tip but also appreciable camber.Conical camber, used on supersonic Convair aircraft, reduces
induced drag in a somewhat similar manner.
Except at maximum speed, i.e., at very low angles of attack, thenew wing should impose virtually no penalty. Moreover it gives
a wing tip which—assuming e.g. problems can be overcome—should form a useful attachment-point for stores of all kinds.
Probably the missions of the P.I are so complex that the optimumwing should, like the powerplant, have variable geometry.
Throughout, minimum drag—and hence minimum overall fuelconsumption—is the primary aim.
It is in such trials that the two P.I As have laid a solid foundationof knowledge for the much more powerful P. IB. They have flown
over 500 missions, recording far more than half the total manned-supersonic time logged by British aircraft (a fact which the
writer considers an indictment of our overall progress as anation). Details of the performance recorded by the two P.lAs
may not be divulged, but Air Marshal Sir Thomas Pike, A.O.C-in-C. Fighter Command, recently stated that the type had exceeded
1,000 m.p.h. (Mach 1.51) in level flight and that the design was"capable of 1,500 m.p.h." (Mach 2.3). No doubt the Air Marshal
meant the latter claim to apply to the P.1B.
As stated at the opening of this account, flight trials with theP.1B have now begun. The first machine, XA 847, flew in "Bea's '
hands between 12.55 and 1.19 p.m. on April 4. In this periodXA 847 flew faster than sound and also posed for the picture on
p. 541. Other very successful flights have since been made.
In the P.IB the powerplants are Rolls-Royce Avons of "anadvanced type," and their high thrust is further increased by the
incorporation of full reheat with a variable-area nozzle. The actualmark of engine fitted may not be disclosed, but it is appropriate
to comment that the RA.24 was recently announced as havingbeen type-tested at 11,250 lb dry thrust without reheat. Suffice to
say that the P. IB has appreciably more than 50 per cent morethrust than the P.I A, and this margin proportionately increases as
the Mach number rises beyond 1.
A study of the three-view general arrangement makes it per-fectly clear that the P. IB fuselage is quite different from that of
its predecessor; in fact it is doubtful if there are many partscommon to both types. Notwithstanding the much more powerful
engines the body of the P.IB is no deeper or fatter than that of theearlier machines.
The front end and intake clearly differs substantially from thecorresponding part of the P.I A. In the only photographs released
for publication full details of the intake are hidden. It is pertinent,however, to note that the lip of the intake suggests a circular form,
and the presence of a long pitot head concentric with the lipsuggests that a centre-body is fitted (and an unofficial published
photograph confirms this). The purpose of the centre-body is tocreate an inclined shock-wave which, under optimum conditions,
is focussed on the lip of the intake. Combined with a normal shockacross the radial gap between the lip and the centre-body this
achieves deceleration of the intake air without a critical loss intotal energy.
Direct pitot intakes (i.e., devoid of a centre-body) are satisfac-tory up to Mach numbers of perhaps 1.3 or 1.35, but begin to fall
off in performance to an unacceptable degree at higher Machnumbers. When the P.I A first flew we commented "technicians
will . . . note, too, that the intake is of plain open-mouth formlacking the central 'bullet' now considered essential for efficient
operation at Mach numbers over 1.3 or so." The complete
From left to right these sketches show: the nose undercarriage of
the P.I A (with the wheel stowed flat); the nose undercarriage of the
P.IB; and the port main undercarriage of the P.1B.